Impacts of heterogeneous organic latter on phenanthrene sorption: Different aquifer depths

Alluvial aquifer samples from the same depth but different locations and fr om different depths at the same location were characterized and evaluated b oth for the nature of their organic matter and their sorption properties. B oth equilibrium and kinetic sorption were evaluated using batch studies wit h phenanthrene. Organic petrology was used both qualitatively and quantitat ively to explain and predict the patterns of sorption for each sample. Orga nic carbon content values varied by 1 order of magnitude, and sorption capa cities varied by 2 orders of magnitude within a given depth and location fo r these samples. The sorption isotherms ranged from nonlinear to virtually linear. The organic content-normalized distribution coefficients (K-oc) var ied significantly between organic matter subgroups as did the time to reach equilibrium. We were able to correlate these Variations in sorption behavi or with the organic matter type in subgroups. K-oc values were assigned to each organic matter subgroup and were used along with the fraction of each organic matter subgroup to predict the composite K-oc values. Close agreeme nt between predicted and measured K-oc values validated this approach. Usin g the subgroup K-oc values and literature fraction organic carbon (f(oc)) v alues, the sorption distribution coefficients were also predicted within th e 95% confidence intervals for the measured values. Our results also demons trate that opaque organic matter fractions dominate the sorption process an d that quantifying this fraction alone can virtually predict the sample K-o c value.